Electrophotographic method



R. s. OLDEN 3,442,645

ELECTROPHOTOGRAPHIC METHOD Filed June 12. 1964 /6 mm- /Z {z 412 j/% 1 rT 1N VEN TOR.

E65? 6 0105 BY M. May

United States Patent US. Cl. 961.4 6 Claims ABSTRACT OF THE DISCLOSURE Amethod of transferring an unfused, visible image of electroscopic tonerparticles from a record to a transfer sheet comprises the steps of (a)charging a dielectric sheet with a uniform electrostatic charge, (b)disposing the record in contact with the transfer sheet with the visibleimage against the transfer sheet, (c) disposing both the record and thetransfer sheet on the charged dielectric sheet, and (d) applyingpressure between the record and the transfer sheet. The charge on thedielectric sheet should be of a polarity to effect a transfer of theelectroscopic toner particles from the record to the transfer sheet. Theapparatus comprises a rotatable dielectric belt disposed betweencharging means and developing means for conveying both transfer sheetsand a charge to the developing means.

This invention relates generally to the field of electrophotography, andmore particularly to an improved method of'and apparatus fortransferring an image on a master electrophotographic record to one ormore transfer sheets. The method and apparatus of the present inventionare particularly useful for making copies of information fromelectrophotographic records produced by an electrophotographic outputprinter of the type proposed for electronic data processing apparatus.

, It has been proposed to transfer the unfused visible image ofelectroscopic particles on an electrophotographic record to a transfersheet by placing one side of the transfer sheet against the visibleimage and exposing the opposite side of the transfer sheet to a coronadischarge of a polarity that attracts the electroscopic particles to thetransfer sheetLWhere the unfused visible image is on a rotatable drumand the transfer sheet is moved against the drum to transfer the imageto the transfer sheet, the corona discharge must be applied atsubstantially the points of contact between the drum and the transfersheet. The method and apparatus of the invention for the charging andmoving of the transfer sheet are even-simpler than the" prior methodsand apparatus.

It is an object of the present invention to provide an improved methodof making one or more copies of an image which is on a masterelectrophotographic record.

' Another object of the present invention is to provide an improvedmethod of and apparatus for making a plurality of copies of an imagewhich is on a master electrophotographic recordat a relatively higherspeed and at a relatively lower cost per copy than has heretofore beenpossible. e

A further object of'the present invention is to provide improved'apparatusby means of which many prior art electrophotographic machinesmay be converted to appar'atus for producing one or more copies of animage which is on a master electrophotographic record.

Still a further object of the present invention i to provide an improvedmethod of copying on transfer sheets of any selected one of manydifferent types an image which is on amaster electrophotographic record.

' Another object of the present invention is to provide an improvedmethod of transferring an image to a trans fer sheet from a masterelectrophotographic record that is relatively easy to carry out, andimproved apparatus by means of which the improved method may beperformed efficiently.

These and other objects are attained, in accordance with the improvedmethod of the present invention, in conjunction with anelectrophotographic process wherein an unfused image of electroscopictoner particles on a' master electrophotographic record is firstproduced. A sheet of dielectric material is provided with anelectrostatic charge of a polarity that will cause the electroscopicparticles that form the image to leave the master record. A transfersheet and the master record are placed in contact with each other withthe image against the transfer sheet, and both transfer sheet and masterrecord are stacked on the charged dielectric sheet. Pressure is appliedbetween the master record and the transfer sheet. The electroscopicpowder of the image is attracted to the transfer sheet by the charge onthe dielectric sheet. The master record is separated from the transfersheet and the visible images on both the master record and the transfersheet may be fixed by heat. If more than one copy of the image on themaster record is desired, the master record may be redeveloped byapplying additional electroscopic toner thereto and the aforementionedmethod can be repeated.

The improved apparatus of the present invention comprises thecombination of a dielectric belt with record supporting means, such as adrum, for developing a master record. The dielectric belt is charged ata point remote from the point of transfer of the image from the masterrecord to the transfer sheet. The dielectric belt serves tWo functions:First, the dielectric belt, when charged, provides efiicient conveyingmeans for holding the transfer sheet firmly to it by electrostaticattraction and for moving it into contact with the image on the masterrecord, and, second, the charge on the dielectric belt provides anelectrostatic force, other than the corona discharge device, forattracting the electroscopic particles on the master record to thetransfer sheet.

The novel features of the present invention, both as to its organizationand method of operation, as well as additional objects and advantagesthereof, will be more readily understood from the following description,when read in connection with the accompanying drawing in which similarreference characters refer to similar parts throughout, and in which:FIGS. 1, 2, and 3 are schematic Sectional views of apparatus forcarrying out the steps of charging, exposing and developing a masterelectrophotographic record in accordance with the improved method of thepresent invention;

FIG. 4 is a schematic sectional view of apparatus for charging adielectric sheet in a step 'of the improved method of the presentinvention; a FIG. 5 is a schematic sectional view of apparatus fortransferring a visible image from a master electrophotographiclrecord toa transfer sheet in 'a' step in the improved method of the presentinvention; j

FIG.'6 is a schematic sectional view of apparatus for redeveloping themaster electrophotographic record after of the present invention; and

a copy has been made in a step in the improvedmethod FIG. 7 is aschematic sectional view of one embodiment of improved apparatus formaking a plurality of copies from a master electrophotographic record inaccordance withthe improved method of the present invention;

- Referring, now, particularly to FIG. 1 'of the drawing,

. there is shown an electrophotographic record 10; hereinafter calledthe master record 10 primarily for purposes of identification. Themaster. record 10 may comprise a flexible substrate 11, such as paper,:and a photoconductive layer 12, such as photoconductive zinc oxidedispersed in a resin binder.

To produce a visible image on the master record 10, a uniformelectrostatic charge is applied to the photoconductive layer 12, in thedark, by a corona discharge device, as shown in FIG. 1. A relativelyhigh voltage, about 6,000 volts, is applied from a power supply 14between one or more thin wires 15 of a shielded corona discharge device16 and a grounded plate 18. The master record is placed on the groundedplate 18. One terminal of the power supply 14 is grounded and the otherterminal is connected to at least one wire 15. Depending upon thepolarity of the terminal of the power supply 14 that is connected to thewire 15, the master record 10 may be charged either positively ornegatively, in a manner known in the art.

The uniformly charged master record 10 is exposed to a light image, asby placing a photographic negative 20 against the master record 10 andexposing the photoconductive layer 12 to a source 22 of light throughthe photographic negative 20, as shown in FIG. 2. The portions of thephotoconductive layer 12 that are exposed to light become conductive anddecrease the electrostatic charge in these portions in proportion to theintensity of the light impinging on them. Thus, an electrostatic latentimage is formed on the photoconductive layer 12.

The electrostatic latent image can be converted to a visible image byapplying electroscopic toner particles thereto, by any suitable meansknown in the art. Referring to FIG. 3 of the drawing, there is shown anelectroscopic developing mixture 24, such as a mixture of tonerparticles of pigmented shellac, for example, and iron filings applied tothe photoconductive layer 12 by means of a magnet 26 to develop theaforementioned latent image thereon. This method of magnetic brushdevelopment is described in U.S. Patent 2,786,439, issued to C. J.Young, on Mar. 26, 1957, for Ele'ctrophotographic Developing Apparatus,and assigned to the assignee of the present invention.

Before transferring the unfused visible image on the photoconductivelayer 12, an electrostatic charge is applied to a dielectric sheet 28,such as a sheet of insulating plastic material of the polyethyleneterephthalate type, of which Mylar is an example. The charge on thedielectric sheet 28 should be of such a polarity that the tonerparticles are repelled from the master record 10 and driven or drawntowards the transfer sheet. In the arrangement shown in FIG. 5, thismeans, that for a direct image on the master record 10, the charge onthe dielectric sheet 28 should be negative, and, for a reverse image onthe master record 10, the charge on the insulating plastic material 28should be positive. A direct image may be defined as one in which theopaque areas in the photographic negative 20 are duplicated as blackareas on the master record 10. A reverse image is one in which thetransparent areas on the photographic negative 20 are printed black onthe master record 10. Regardless of which method isused,

the image on the transfer sheet 30 is always a true facsimile of theimage on the master record 10. The electrostatic charge can be appliedto the dielectric sheet 28 by means of the corona discharge device 16,energized by the power supply 14, as shown in FIG. 4.

The unfused visible image of electroscopic particles on thephotoconductive layer 12 of the master record 10 can be transferred to atransfer sheet 30, such as a sheet of paper, for example, by placing thetransfer sheet 30 on the previously charged dielectric sheet 28, and byplacing the master record 10 on the transfer sheet 30 with the visibleimage in contact with the transfer sheet 30. Pressure is then appliedbetween the master record 10 and the transfer sheet 30 by any suitablemeans, as by a roller 32 adapted tobe pushed manually across the top ofthe master record 10 in the direction of the arrow 34, as shown in FIG.5. The amount of pressure used is not critical, but there'should beenough pressure applied to provide good contact'between the masterrecord 10 and the transfer sheet 30. The charged dielectric sheet 28attracts the electroscopic toner particles of. the visibleimage on thephotoconductive layer 12 of the master record 10 and transfers them tothe transfer sheet 30, thereby effecting a transfer of the visibleimage. More than one copy of the visible image on the master record 10is possible by redeveloping the master record 10, as shown in FIG. 6, aslong as the electrostatic latent image is present on the photoconductivelayer 12. The redevelopment of the master record 10 shown in FIG. 6 issubstantially similar to the original development of .the master record10, as shown in FIG. 3. The number. ,of times the master record 10 maybe redeveloped may depend upon the ambient temperature and humidity, themoisture content of the transfer sheet, and the time of each cycle ofdevelopment.

Referring, now, to FIG. 7 of the drawing, there is shown an embodimentof the improved apparatus for making one or more copies of a visibleimage on a master electrophotographic record 10a, a portion of a web ofelectrophotographic record material. The master record 10a may besimilar in composition to the master record 10. The master record 10a isa continuous web of material" from which sheets of desired lengths maybe cut. The web of the master record t10a is unwound from a supply roll32, passed over idler rollers 34 and 36, and pulled between a pressureroller 38 and a driven roller 40. The web of the master record 10a ismoved over a window 42 of a thin window cathode ray tube TWCRT forexposing the photoconductive surface 12a of the master record 10a in'amanner described by the instant inventor in RCA Review, September 1961,vol. XXII, No. 3. The photoconductive surface 12a of the master record10a is disposed preferably against the window 42. Where the masterrecord 10a is translucent, its photoconductive surface 12a maybe exposedfrom either surface of the master record. While the thin window cathoderay tube is illustrated herein as means for exposing the master record10a, any suitable means of electromagnetic radiation known in the artfor exposing the master record may be employed.

In order to prevent excessive frictional wear of the thin window 42 bythe web of the master record 10a, a web oftransparent plastic material44, having a relatively low coeflicient of friction, such as Mylar, isdisposed between the master record 10a and the thin window 42 of thecathode ray tube TWCRT. The web of plastic material 44 is unwound from asupply roll 46, passed over an idler roller 48,- and pulled by a drivenwind-up roller 50 Thus, the master record 10a can be exposed tolight-from the cathode ray tube through the window 42 and thetransparent plastic material 44.

t The photoconductive surface 12a of the master record 10a, before beingexposed to light, is provided with a uniform electrostatic charge by acorona discharge device 16 disposed adjacent to the master record 10a.The corona discharge device 16 is provided with the usual power supply,not shown for the sake of simplicity. Thus, upon exposure to light fromthe electron beam at the window 42, an electrostatic latent image isproduced on the photoconductive surface 12a' of the master record 10a.

After exposure, a suitable length of the web of master record 10a iscut, as by shears 52, and fastened to the cylindrical surface of arotatable drum 54 by any suitable means, such as by adhesive tape or bysuction means (not shown) of the type used in the printing arts. Thedrum 54 is disposed for rotation about its axis and is rotated by anysuitable means, such as a motor (not shown).

The electrostatic latent image on the photoconductive surface 12a of themaster record 10a is developed by moving it over a cylindrical brush 56disposed to rotate about its axis in a trough 58 of electroscopicdeveloping mixture 24. Any iron filings'from the developing mixture 24remaining on the master record 10a after development can be cleaned upby'an electromagnet 60 disposed adjacent to the developed master record10a on the drum 54. The master record a"rotates with the drum 54 throughany number of desired revolutions, depending upon the number of copiesof the unfused electroscopic image thereon to be made.

Means are provided to transport transfer sheets 30 from a stack 62 oftransfer sheets to the drum 54 for contactwith'the image of unfusedelectroscopic toner particles on the developed (toned) master record10a. To this end, there is provided a belt 28a of dielectric material,similar to the aforementioned dielectric sheet 28, such as Mylar, forexample, The belt 28a is disposed around an idler roller 64 and a drivenroller 66 for rotation thereabout. The roller 66 presses the belt 28aagainst the master record 10a on the drum 54. When an electrostaticcharge is applied to the belt 28a, as by a corona discharge device 16a,the belt 28a becomes an eflicient conveyor for a transfer sheet 30because the latter adheres to the belt 28a by electrostatic attraction.The corona discharge device 16a is disposed at a point remote from thepoints of contact 48a between a transfer sheet 30 on the belt 28a andthe master record 10a on the drum 54.

To transfer the visible image on the master record 10a to a transfersheet 30, an electrostatic charge from the corona discharge device 16ais applied to the dielectric belt 28a, and a sheet 30- is placed on thebelt 28a. The sheet 30 adheres electrostatically to the belt 28a and ismoved thereby into contact with the master record 10a on the drum 54.The drum 54 and the roller 66 are moved synchronously, by any meansknown in the art. The charge applied to the dielectric belt 28a shouldbe of a polarity opposite to that of the electroscopic toner particlesin the developing mixture 24 if a positive image is desired. Thus, whenthe transfer sheet 30 is brought into contact with the image ofelectroscopic toner particles on the master record 10a, as at points48a, the charged belt 28a functions to attract the charged electroscopicparticles from the visible image on the master record 10a to thetransfer sheet 30. Thus, in addition to serving as-a conveyor belt,holding the transfer sheet 30 thereto by electrostatic attraction, thebelt 28a also functions as an electrostatic force means to attractelectroscopic toner particles whereby'to effect a transfer of the imagefrom the master record 10a to the transfer sheet 30'.

The radius of curvature of the roller 66 is small enough so that thetransfer sheet 30 can not follow the belt around the roller 66. Forexample, when the diameter of the roller 66 is smaller than 1 and /2inches, ordinary paper will not follow a Mylar belt 28:; around theroller. Thus, the transfer sheet 30 leaves the roller 66 and falls intoa chute 68. A slide 70 at the bottom of the chute 68 is adapted toretain the transfer sheet 30 therein so that it may be exposed to heatfrom a fuser 72 disposed on one side of the chute 68 and adapted toradiate suflicient heat to fuse the transferred image on the transfersheet 30. The sheet 30 is allowed to fall into an exit chute 74 througha slot 76 in the slide 70 after the transferred image has been fused onthe transfer sheet 30.

Additional copies may be made of the image on the master record 10a byredeveloping the master record 10a and pressing another transfer sheet30 into contact with the image of electroscopic toner particles by meansof the charged dielectric belt 280. Thus, by redeveloping the samelatent electrostatic image on the master record 10a for each additionalcopy on the transfer sheet 30 desired, a plurality of copies of an imageon the master record 10a may be made, Four copies of good quality havebeen obtained by transfer from a master record 1011, redeveloping themaster record 10a after each transfer and using a master record and adeveloping mixture of the type described in the aforementioned patent.When the master record 10a is no longer needed, it may be stripped fromthe drum 54 and allowed to fall onto an exit guide 78. The image on themaster record 10a may be 'fused and kept as a reference, if desired.

It is apparent from the aforementioned description of the method andapparatus of the present invention that the image transferred to thetransfersheet is a mirror image of that on the master record. If theimage on the transfer sheet is to be an exact representation of theobject that the image portrays, the image on the master record should bea mirror image of the true object. The latter results are easilyobtained by using the proper number of lenses and/ or mirrors in amanner well known in the electrophotographic and photographic arts formaking a mirror image of a true object on a master record.

From the foregoing description, it will be apparent that there has beenprovided an improved method of and apparatus for transferring an imageon a master record to one or more transfer sheets. Since the transfersheet can be almost any kind of sheet mateial, the cost per copy isrelatively low. Although the embodiment of the apparatus for carryingout the method is one that is particularly applicable for making copiesfrom master records produced by an electrophotographic output printer ofthe type proposed for electronic data processing equipinent, theimproved arrangement of the dielectric belt and the corona dischargedevice for charging the belt with res ct to the means for carrying anddeveloping the master record may be applied to many prior artelectrophotographic processing apparatuses. Thus, while only oneembodiment of the invention has been described and shown in diagrammaticform, variations in its structure coming Within the spirit of thisinvention will, no doubt, readily suggest themselves to those skilled inthe art. Hence, it is desired that the foregoing shall be considered asillustrative and not in'a limitmg sense.

What is claimed is:

1. In an electrophotographic method wherein an electrostatic latentimage on an electrophotographic master record is developed with anelectroscopic toner of one polarity to produce an unfixed visible imagewhich is then transferred to a transfer sheet, the improvement of makinga copy of said visible image on said transfer sheet, with the aid of adielectric sheet, comprising the steps of charging said dielectric sheetwith an overall-electrostatic charge of a polarity opposite to said onepolary,

disposing said transfer sheet against said charged dielectric sheet,

disposing said master record against said transfer sheet with saidvisible image facing said transfer sheet, and

applying pressure between said master record and said sheets.

2. In an electrophotographic method wherein an electrostatic latentimage on an electrophotographic master record is developed with anelectroscopic toner to produce a visible image of said latent image, theimprovement of making copies of said visible image on transfer sheets,with the aid of a dielectric sheet, comprising the steps of chargingsaid dielectric sheet with an overall electrostatic charge,

disposing one of said transfer sheets against said charged dielectricsheet,

disposing said master record against said one transfer sheet with saidvisible image facing said onetransfer sheet,

applying pressure between said master record and said sheets,

separating said master record, said one transfer sheet,

and said dielectric sheet from each other, redeveloping said masterrecord with said toner, disposing another of said transfer sheetsagainst said charged dielectric sheet and said master record on saidother transfer sheet with the redeveloped image against said othertransfer sheet, and

applying pressure between said redeveloped master record and said othertransfer sheet. 3. A method of electrostatic recording comprising thesteps of applying an electrostatic charge separately to a master recordand to a dielectric sheet,

exposing said master record with a light image to produce a latentelectrostatic image thereon,

applying an electroscopic toner to said latent image to produce avisible image on said master record,

placing said transfer sheet on said charged dielectric sheet,

placing said master record on said transfer sheet with said visibleimage against said transfer sheet, and

applying pressure between said master record and said sheets whereby totransfer some of said toner of said visible image to said transfersheet, the polarities of said electrostatic charge and saidelectroscopic toner being such as to apply a force to said electroscopictoner to effect the transfer of said visible image from said masterrecord to said transfer sheet.

4. A method of electrostatic recording comprising the steps of applyingan electrostatic charge of one polarity separately to a master recordand to a dielectric sheet,

exposing said master record with a light image to produce a latentelectrostatic image thereon,

applying an electroscopic toner having a polarity opposite to said onepolarity to said latent image to produce a visible image on said masterrecord,

superimposing said transfer sheet on said charged dielectric sheet andsaid master record on said transfer sheet with said visible imageagainst said transfer sheet,

applying pressure between said master record and said sheets, whereby totransfer some of said toner of said visible image to said transfersheet, and

heating the transferred image on said transfer sheet to fuse saidtransferred image thereon.

5. An electrostatic duplicating method comprising the steps of fir sheetwith said toned image against said transfer s eet, applying pressurebetween said master record and said sheets, whereby to transfer some ofsaid toner of said visible image to said transfer sheet,

separating said master record, said first sheet and said dielectricsheet from each other,

applying said electroscopic toner again to said latent image remainingon said photoconductive layer to redevelop said master record,

disposing another of said transfer sheets against said chargeddielectric sheet and said redeveloped master record against said othertransfer sheet with said layer against said transfer sheet, and

applying pressure between said redeveloped master record and said othertransfer sheet. 6. In an electrophotographic method wherein anelectrostatic latent image on an electroph'otographic master record isdeveloped with an electroscopic toner to produce a visible image of saidlatent image, the improvement of transferring said visible image to atransfer sheet, with the aid of a dielectric material, comprising thesteps of,

applying an electrostatic charge to said dielectric material,

superimposing said transfer sheet against said master record with saidvisible image of electroscopictoner facing said transfer sheet,

disposing said superimposed transfer sheet and master record on saiddielectric material, and

applying pressure between said dielectric material, .said

master record, and said transfer sheet, the polarity of saidelectrostatic charge applied to said dielectric material being such asto apply a force on said electroscopic toner to effect the transfer ofsaid visible image from said master record to said transfer sheet.

References Cited UNITED STATES PATENTS 2,576,047 11/1951 Schalfert96-l.4 2,756,676 7/1956 Steinhilper 117l7.5 X 2,812,709 11/1957 Gundlach11717.5 X 2,955,052 10/1960 Carlson et a1. 117l7.5 2,982,647 5/1961Carlson et a1. 961 3,124,457 3/1964 Schwertz 96-1 3,267,840 8/1966 Honmaet a1. 96-1 X 3,288,605 11/1966 Macklem 961 3'. TRAVIS BROWN, PrimaryExaminer.

C. E. VAN HORN, Assistant Examiner.

U.S. Cl. X.R.

